In general, in an electric power steering control device, an assist torque which is approximately proportional to a steering torque is determined. A torque proportional gain indicating the proportional relation is set large. In this manner, a steering torque of a driver of an automobile is reduced, while an appropriate steering feeling is given. Further, in the electric power steering control device, a vibration due to a cogging torque generated by a motor, pulsations generated in synchronization with teeth of a gear, a disturbance transmitted from a road surface, and the like are required to be suppressed to improve a feeling (vibration feeling) of the driver.
As the conventional electric power steering control device for achieving the object described above, there is known an electric power steering control device including a low-pass filter (LPF) and a high-pass filter (HPF) (for example, see Patent Literature 1). Then, a steering component is extracted by the LPF to perform assist torque control. Then, a high-frequency vibration component is extracted by the HPF. Another controller (another gain) different from that for the low frequency is used for the extracted component to perform control.
As another conventional electric power steering control device, there is known an electric power steering control device which relates to control for suppressing the transmission of a disturbance such as a brake vibration input from a tie rod, which is connected to a wheel, to a steering wheel (for example, see Patent Literature 2). In Patent Literature 2, a configuration as follows is adopted to reduce the effects on steering control. Specifically, for a steering-torque signal, a steering component is attenuated by using the HPF of second or higher order. Further, through use of the signal as an input, a control amount is computed by a control-amount map having a large dead zone. In this manner, the steering component is reduced.
Moreover, the configuration includes three gain maps respectively based on a steering torque, a steering speed, and a vehicle speed so that the steering component is further reduced by setting the control amount to zero when the steering torque is large, the steering speed is large, or the vehicle speed is low.